Styrene-maleic anhydride copolymers are typically made by solution polymerization in the presence of aromatic hydrocarbon solvents or ketone solvents. In addition to the solvents being environmentally undesirable, recovering the styrene-maleic anhydride copolymers from the solvent requires additional process steps. For example, aromatic solvents used in the solution polymerization generally require a decanting and drying step prior to recovering the copolymer product, and ketone solvents generally require a solvent-stripping step prior to recovering the copolymer product.
U.S. Pat. No. 3,485,762 describes a process for preparing styrene-maleic anhydride copolymers which are used in a detergent formulation containing polyethylene glycol. The styrene-maleic anhydride copolymers are prepared by solution polymerization using incremental feed addition of the styrene and maleic anhydride monomers and catalyst into a reactor containing an aromatic solvent. The polymerization is conducted at the reflux temperature of the monomers and solvent mixture. The copolymer is isolated and mixed with polyethylene glycol in a detergent formulation. The styrene-maleic anhydride copolymers are present as a physical mixture with the polyethylene glycol and as a partial ester of the polyethylene glyol and styrene-maleic anhydride copolymer.
U.S. Pat. No. 5,158,996 describes a process for preparing styrene-maleic anhydride graft copolymers by solution polymerization in a ketone solvent. The copolymer is isolated and reacted with polyethylene glycol to form a copolymer product containing a styrene-maleic anhydride main backbone chain having polyethylene glycol side chains.